The proposed research will study normal and pathological human auditory nerve action potentials (APs) recorded from external auditory meatus and brainstem evoked response (BERs) recorded from vertex. The project includes investigations relevant to the problems of utilizing these responses to quantify auditory system pathology (by predicting the pure-tone audiogram) and to localize it. Cochlear excitation patterns generated by filtered clicks will be determined with the derived AP technique and supplemented by computer modeling. The relationship between filtered-click AP and BER waveforms and thresholds and the underlying cochlear excitation patterns will then be determined. The ability filtered-click AP and BER thresholds and waveforms to predict pathological cochlear excitation patterns and thence pathological pure-tone audiograms will then be tested in patients with hearing loss. The project also includes research designed to refine and expand previous results which suggest that "square-wave" click AP and BER Latency-Intensity (L-I) functions provide a clinically useful means of separating cochlear from retrocochlear pathology. Data will be collected from a larger series of patients than presently available to confirm the validity and improve the accuracy of the retrocochlear signs derived from the L-I functions and also to test hypothetical AP/BER L-I patterns indicative of conductive hearing loss.